Prevention of corrosion



Patented Apr. 6, 1954 UNITED STATES PATENT OFFICE PREVENTION OF CORBOSIUN poration of Maine No Drawing. Application October 26, 1951, Serial No. 253,459

4 Claims.

'My invention relates to the prevention of corrosion in oil wells. In particular, I have found that palm oil will effectively inhibit the rusting of metallic equipment in a well when added to the well fluids in exceedingly small proportions. The crude oil product obtained from a well in which the Well fluids have been treated with small amounts of palm oil also possesses favorable corrosion-inhibiting properties and so reduces or prevents corrosion in surface equipment, for example, in the connecting pipe lines through which the crude product is transported to the refinery. Palm oil is particularly useful for treating wells producing sour crudes, that is, well fluids containing relatively large amounts of sulfur or sulfur compounds, since such wells present the majority of corrosion problems.

Some degree of corrosion takes place in the metallic equipment of practically all oil wells and in certain environments corrosion may reach costly proportions. ihe casing, tubing and rod strings are all subject to corrosion. The sucker rods and sucker rod boxes which operate under heavy cyclic load conditions are particularly susceptible to failure through corrosion fatigue. As a result of corrosion, costs may be greatly increased because of the necessity of pulling the well sucker rod and tubing string for overhaul and the replacement of the equipment retired. Indirect costs in terms of production losses while replacing such pipe string sections and other equipment may also be considerable.

Recognition of the oil well corrosion problem is comparatively new. However, the most effective method of corrosion control appears to reside in the use of chemical inhibitors. The use of such chemicals has the distinct advantage over other methods that all parts of the well fluid system can be protected.

I have discovered that the corrosive effects of the well fluids on metallic surfaces can be substantially reduced and in many cases practically eliminated by introducing an exceedingly small proportion of palm oil into the well fluids. When palm oil is added to the well fluids I believe it forms a protective coating on the metallic surfaces of the well which are exposed to the well fluids and thereby reduces or eliminates corrosion by preventing the corrosive elements of the well fluids from contacting these exposed metallic surfaces. The palm oil is water insoluble.

I have found that the palm oil used to inhibit the corrosive effects of the well fluids may be fresh palm oil or discard palm oil. Discard palm oil is the waste or spent palm oil discarded from iii plating operations in the manufacture of plated steel products, for example, the hot dip tinning of sheet steel, after the palm oil has lost its effectiveness to produce a good quality plate. Although the use of either fresh palm oil or discard palm oil as a corrosion inhibitor produces substantially equivalent results, I prefer to use discard palm oil as the corrosion inhibitor in the practice of my invention because of its much lower cost. The cost of discard palm oil is about one-fifth the cost of fresh palm oil at the present time. However, in describing my invention I have used the term palm oil to include both fresh palm oil and discard palm oil because in terms of effectiveness as corrosion inhibitors they are substantially equivalent materials.

Palm oil does not hav any toxic or other injurious effects on operating personnel as do some of the other corrosion inhibitors used, for example, formaldehyde. In addition, palm oil does not interfere with oil production, such as by the formation of undesirable clogging or contaminating materials, either at the well or later at the refinery.

The amount of palm oil that must b added to the well fluids to substantially reduce or eliminate corrosion is in the range of approximately 1 to 15 pints per one thousand barrels of well fluid, i. e., crude oil plus brine. The upper limit of this range is arbitrarily set because of economic considerations. The palm oil may be added to the well fluids by merely injecting the desired amount down the annulus between the production tubing and the casing so that it rises with the well fluids. When palm oil is added to the well fluids in proportions within the above range, it also gives favorable corrosion-inhibiting properties to the crude product and thereby inhibits corrosion of the metallic surfaces of any surface equipment with which the crude product comes in contact, for example, the connecting pipe lines to the refinery.

The palm oil can be used as such or can be diluted with a suitable solvent for greater ease of handling. I have found it convenient to employ a palm oil-solvent mixture containing 10 to 20 per cent of a suitable solvent such as kerosene.

As stated above, the effective amount of palm oil, on a solvent-free basis, to substantially reduce or eliminate corrosion is between about 1 and 15 pints per one thousand barrels of well fluids. Expressed in another way, thi is equivalent to about 3 to 45 parts of palm oil per million parts of well fluids. Less than the minimum amount is generally ineffective to reduce corrosion eiTects to any substantial degree while the use of over the maximum amount is unnecessary and wasteful.

The actual amount of palm oil employed as a corrosion inhibitor in any particular case will vary within the 'rangeof about 1 to '15 pints per one thousand barrels of well fluids depending on the corrosiveness of the Well fluids, the resistance of the metallic surfaces to corrosion and the production rate encountered. In addition, flow interruptions and varying temperatures and pressures are capable of affecting the corrosion rate considerably. Of course, the regulation of the proper inhibitor concentration is best determined by an actual measure of corrosion which can be best determined in the last analysis by the actual deterioration in the physical condition of the metallic surfaces exposed to the well fluids. However, it is not practical to rely on such visual inspections since the damage to the well equipment has then already occurred. Accordingly, metal test blanks may beinserted into the stream of well fluid-s and removed and examined at :periodic intervals. Direct measurement of the well fluid acidity is also possible, or a measurement of the iron content of the well fluid may be made since this is an indication of the metal lost through corrosion.

The followin example will illustrate the effectiveness of palm oil as a corrosion inhibitor and will also illustrate its efiectiveness as compared toa-nother corrosion inhibitor. However, it must be realized that the test of the example was run on a specific well 'fluid'and that the extreme variations found among well fluids as well as the variation in rates and conditions of production of oil wells in the same and different oil fields are factors which must be considered. Also, it is well known that a particular inhibitor may show superior corrosion inhibiting properties over other corrosion inhibitors in a particular well or field and yet show inferior corrosion inhibiting properties with respect to the same other corrosion inhibitors in a difierent well or field. Consequently, oil well corrosion inhibitors are customarily selected for use in a particular well or field according to the conditions encountered in that well or field, and even then the superiority of a particular inhibitor over other inhibitors is unpredictable.

The following'example shows a comparison between the corrosion inhibiting properties of palm oil and an oil solution "of a commercially used sulfonate-type corrosion inhibitor. This latter inhibitor which I shall refer to as inhibitor A has the following test characteristics:

Gravity, API 28.0 Flash, F 385 Fire, F 445 Viscosity at 100 SUS 416 Viscosity at 130 SUS 163 Viscosity at 210 SUS 49.2 Viscosity index 90 Color 4% Nitrogen (per cent) 0.265 Acid number 9.0 Sulfur (per cent) 0.60

Example I I compared the corrosion-inhibiting properties of palm oil and inhibitor A by means of a modification of the ASTM test for Rust-Preventing Characteristics of Steam Turbine Oil in the Presence of Water D665-47T. In the modification, a weighed metal test coupon was exposed in rapidly stirred well fluid or a blend of that well fluid plus an inhibitor. The test was run at room temperature for 24 hours after which the metal test coupon was removed from the test solution, cleaned to remove corrosive products, and reweighed.

The concentration of both palm oil and inhibitor A employed in the test runs was 0.02 weight per cent (on a solvent free basis) based upon total fluid, i. e., crude oil plus brine.

Corrosion losses, expressed as milligrams of corrosion per square decimeter of surface per day (m. d. d), were as follows: Blank test without any inhibitor, .128 m. d. d.; test with palm oil present, '52 m. d. d.; and test with inhibitor A present, 70 m. d. d.

The results show that the test employing inhibitor A produced a corrosion rate approximately per cent greater than the rate when palm oil was employed, while the test without any inhibitor produced a corrosion rate approximately 250 per cent of the rate found when palm oil was present. In the above test the palm oil employed was fresh palm oil. However, as I have stated previously, fresh palm oh and discard palm oil give substantially equivalent results when em- .ployed as corrosion inhibitors. I prefer to use discard palm oil because of its much lower cost.

I claim:

1. In the production of oil from wells, thestep of introducing palm oil into the well fluid in an amount of about v1 to 15 pints per one thousand barrels of well fluid.

2. Crude oil to which favorable rust inhibiting properties have beenimparted by the addition of about 1 to 15 pints of palm oil per one thousand barrels of well fluid.

3. In the production of oil from wells, the step of introducing discard palm oil into the Well fluid in an amount of about 1 to 15 pints per one thousand barrelsof well fluid.

4. Crude oil to which favorable rust inhibiting properties have been imparted by the addition of about 1 to 15 pints of discard palm oil per one thousand barrels'of well fluid.

References Cited in the file of this patent UNITED STATES PATENTS Name Date *Calcott'et al Mar. 25, 1930 OTHER REFERENCES Lewkowitsch, Chemical Technology and Analysis of Oils, Fats and Waxes, vol. II, page 548, published 1914 by MacMillan and Co. of London.

Hock, Corrosion Problems, article in The Oil Weekly, Jan. 27, 1947, pp. 33 35.

Thornton, Remedies Studied for Freakish Corrosion, article in Petroleum Processing, April 1947, pp. 273,275, 276, and 279.

Shock, pr; Determination in Condensate 'Well Waters, article in World Oil, July 1948, Production Section, pp. 141 andl42.

Baker 'et al., Polar-Type Rust Inhibitors, article in Industrial and Engineering Chem., vol. 40, pp. 2338-2347, December 1948.

Shock et al., Prediction of Corrosion in Oil and Gas Wells, article in the Petroleum Engineer- Refiner Annual, 1951, pp. 3-86. 3-88, B 90, SB-92, B494, B-96, and i3-98.

Number 

1. IN THE PRODUCTION OF OIL FROM WELLS, THE STEP OF INTRODUCING PALM OIL INTO THE WELL FLUID IN AN AMOUNT OF ABOUT 1 TO 15 PINTS PER ONE THOUSAND BARRELS OF WELL FLUID. 